[feature request] ability to use pki sign endpoint in vault

It would be really nice if consul-template would support not just pki issue but also pki sign endpoint in vault.

When one has a system with a lots of clients and a low cert ttl, the amount of private key generation can cause quite a heavy load on the vault side in the case of pki issue, however if one uses the pki sign endpoint the private key generation remains on the client side, I made a PR about this some time ago, could this get a bit of attention?

https://github.com/hashicorp/consul-template/pull/1905

Start by reviewing pull request #1905, which is linked in the issue, and trace how consul-template currently supports Vault's PKI issue endpoint. Confirm the intended support for Vault's PKI sign endpoint and use the existing request path and tests as the completion reference.

Written by the indexing model from the issue text.